The primary purpose of this study is to determine the frequency of heterozy sity for Tay-Sachs disease in persons of French-Canadian background in New Engla , specifically Vermont. An attempt will be made, using this data and data fr the other New England states, to determine any regional variation in the freque y of heterozygosity due to different French-Canadian migration patterns. The ata will then be disseminated to primary care physicians and genetic centers throughout the region.